Forainiferal biostratigraphy of the Egerian flysch sediments in the Silesian Nappe, Outer Carpathians, Polish part of the Bieszczady Mountains

Abstract

Biostratygrafia otwornicowa utworów egeru płaszczowiny śląskiej Karpoat zewnętrznych w polskiej części Bieszczadów Planktonic and benthic Foraminifera have been studied from the youngest deposits of the Krosno beds in the inner part of the Silesian Nappe (Outer Carpathians) in the Bieszczady Mountains. The studied part of the Krosno beds consists of Egerian (upper Oligocene–lower Miocene) flysch sediments, deposited within the Outer Carpathian Basin, a part of the Central Paratethys. Two interval zones: Tenuitella munda Zone and Globigeri- nelloides primordius Zone have been distinguished basing on the succession of planktonic Foraminifera. Additionally, Paragloborotalia inaequiconica Interval Subzone has been defined within the first one. Occurrence of calcareous nannoplankton, dinocyst assemblages and isochronous horizons of coccolith limestones (the Jasło Limestone and Zagórz Limestone) enabled correlation of the planktonic foraminiferal zones with chronostrati- graphy. The boundary between the two distinguished zones corresponds to the base of NN1 nannoplankton Zone (defined by the occurrence of Helicosphaera scissura) equivalent to the Oligocene/Miocene boundary. The base of the P. inaequiconica Subzone corresponds to the position of the Zagórz Limestone, refferred to NP 24 Zone (early Egerian). The benthic foraminiferal assemblages are dominated by bathyal, calcareous, hyaline, smooth-walled taxa, indicative of anoxic environment. The benthic assemblages remained relatively stable throughout the late Oligocene and were more diversified during the earliest Miocene, most probably in response to the oxygenation of bottom waters, due to the opening of new connections between the Central Paratethys and the Mediterranean region.